This invention relates to the vulcanization and bonding of tire components, more particularly it relates to the use of induction heating to assist in the curing or bonding of said tire components.
Generally tires are cured in a process known as vulcanization whereby elastomeric material is heated in molds. The heated molds are generally conductive in nature and transfer heat from the surface of the tire to the internal components requiring a fixed amount of time at a given temperature in order to achieve full complete curing of the tire.
Rubber or elastomeric material is not an effective conductive material and acts as somewhat of an insulator. Therefore, for a complete curing of a tire to occur, many of the components are over cooked or exposed to a larger amount of heat than normally would be required if the tire would quickly and uniformly achieve curing temperature. Due to the various time lengths involved in the curing process to bring all of the material up to curing temperature the vulcanization process requires many minutes to completely cure a tire. In European patent publication 0183450A2, Anthony James Sumner devised a mold which would permit a tire to be cured using electric current which may be induced electromagnetically. The mold itself had a variety of insulating segments and side plates which permitted varying amounts of conductive heat to be applied to the mold in such a fashion that selective regions of the tire could achieve more heat in such areas where the tread and bead are thicker. The mold itself was a rather complicated structure which did permit an electromagnetic curing of the entire tire structure. The mold however provided the selective curing capability of the tire for thick and thin regions.
In U.S. Pat. No. 5,483,043 assigned to General Electric Company, inducting heat of polymer matrix composites mold press was disclosed wherein electrically conductive fibers were added to the polymer matrix to facilitate the induction heating of the polymer. This patent deals with polymeric matrix that generally fall into two classes, thermosetting and thermoplastic which are fiber loaded. Examples of materials typically for reinforcing fibers include carbon graphite, barons, and silicone carbide. It is believed that the polymeric components manufactured under General Electric Company""s patent related to the aircraft industry and did not include nor encompass rubber tire components.
In a Japanese patent application more relevant to the rubber industry Patent No. JP8216289A discloses a method of retreading tires using high frequency waves to vulcanize the adhesive layer incorporating the base tire with the reheating member. In this patent the steel cords in the belt layers are heated by activating or inducing an inductive heating coil which heats the steel cords and in turn provides a heat source for the curing of the cushion gum used in the retreading of the tire. While this method of using induction heating provides the use of the tire cords as the inductively heated metal component it is recognized that such cords have limited surface area and the heat transfer is rather localized around the belt cords.
The most relevant patent is Japanese Patent Publication 128764 which recites a method of curing a tire component using the steps as recited in the preamble of claims 1 and 6, the portions thereafter the characterizing clause represents the novel features of the present invention. The dependent claims describe features of the preferred embodiments of the invention.
In document JP 09 207241 a cushion gum is described having a magnetic powder of 5 parts by weight or more for use in retreading tires.
It is an object of the present invention to find a uniform dispersal of fibers susceptible to inductive heating throughout a tire component so that the tire can be selectively cured. It is a further object of the invention to provide a preformed rubber component having fibers which are susceptible to inductive heating that will permit the tire to be more rapidly cured when used in combination with conventional curing methods.
A method of selectively curing tire components (10, 20, 3040) has the steps dispersing of plurality of metal particles (12) or short fibers (12) into a rubber composition (14). Preferably, the dispersion of the plurality of metal particles (12) or short fibers (12) into a rubber composition (14) includes the step of a extruding the material while blending in the fibers (12) or metal particles (12).
The fiber loaded rubber composition is then preshaped into a tire component (10, 20, 30, or 40) of a predetermined cross-section. Then the tire component can be placed in an induction heating coil and the heating coil can be activated thereby internally curing the tire component while maintaining the external surfaces of the tire component partially or completely uncured.
In order to achieve this selective curing of tire components, it is further contemplated that one would preselect a time and energy profile for a particular tire component to insure the external components remain at least initially uncured while the interior of the tire component is cured.
Several alternative methods of selectively curing tire components (10, 20, 30, or 40) further have the steps of placing the preshaped tire component with fiber or metal particles (12) disposed throughout into an assembly of tire components prior to applying induction heating. The entire tire assembly (2) is then placed in an induction coil which is activated thereby heating the fiber laden component and then after curing or partially curing that component (10, 20, 30, or 40), one finishes the curing of the tire assembly (2) in a conventional mold curing press.
Alternatively, the placing of the preshaped fiber loaded tire component into an assembly (2) of tire components prior to applying induction hearing can include the step of placing the tire assembly (2) in a conventional curing press and curing all the uncured external surfaces of the tire (2) and then placing the tire (2) in an induction coil and applying induction heating to finish cure the preshaped tire component or components (10, 20, 30, or 40). In another method, the preshaped tire components loaded with fibers or metallic particles (12) can be assembled within an assembly of other tire components prior to applying induction heating and then placing the entire tire assembly (2) in a mold curing press and simultaneously providing conductive and induction heating to cure the tire components and the tire assembly in a single curing process.
In a preferred embodiment of the invention, the preshaped component will be premixed with induction sensitive particles (12) such as iron, nickel, oxides of iron, nickel, etc. When such fibers (12) are loaded into a rubber compound (14) and dispersed through an extrusion process or some other method, as little as a fraction of one percent to five percent of fiber (12) per 100 parts by weight of rubber is needed in order to achieve a high dispersion of induction sensitive material throughout the composition. This minimal amount of fibers (12) enables the component (10, 20, 30, or 40) to be rapidly heated thus permitting the selective curing described above.